I bought my dining chairs for my back porch chairs on Wayfair. They have been great! Easy to clean, durable and stack for storage in the winter. Wayfair has a great selection of patio sets and individual items if you want to mix and match.
I just bought a bunch of patio furniture on Wayfair, Target, and Overstock. I've been pleased with all of it. I haven't had the chance to give it the endurance test yet, but so far so good! Aesthetically it's all appeared to be decent quality. I will say that assembly is often more frustrating with lower priced items. We had some chairs from Overstock that would NOT go together because the holes for the legs were improperly drilled. Overstock has been mostly helpful, but it's a hassle to ship things back.
I like to mix second-hand items with new purchases. I always buy my patio umbrella new (used ones tend to be pretty unreliable.) My current one is from Lowes. I need a new table and am hunting for one at thrift stores. Most tables can be easily hacked by drilling a hole in the middle for the umbrella :)
We love teak outdoor furniture because it's easy care and long lasting. Throw on some bright colored cushions and you have a high quality and trendy ensemble. Finish it all off with a polypropylene outdoor rug...their so durable!